But of the complaints that may be lodged against the displays, the most damning may be that they’re ineffective. The now-extensive research into caloriedisplays hasn’t yet turned up consistent, compelling evidence that they significantly curb unhealthy eating habits—at least on their own.

Now there may be another approach, based on the same logic that maintains order at traffic intersections around the world: people respond to color. A new study published Aug. 6 in the American Journal of Preventative Medicine suggests that when it comes to nutrition, people may pay more attention to simple color-coded warnings: Green for healthy, yellow for less so, and red for calorie bombs.

“The cool thing about this is that it is really simple and straightforward,” said Douglas Levy, the study’s lead author, as well as an assistant professor of medicine at Harvard Medical School and a researcher at the Mongan Institute of Health Policy at Massachusetts General Hospital. “It does not require a revolution.”

The study took place on Levy’s home turf: the MGH cafeteria, used by the hospital’s employees, patients, and visitors. In phase one, the researchers applied nutritional color labels to the items in the cafeteria. (When the labels were first introduced, dieticians were on-hand to explain them to customers.)

Phase two involved a so-called choice architecture intervention. Simply put, the cafeteria’s offerings were rearranged, with more healthy foods and beverages placed closer to customers’ natural reach and lines of sight, and less healthy options made slightly less convenient to access.

Thanks to the “platinum cards” used by MGH employees, which allow them to buy food at the cafeteria by deducting the cost directly from future paychecks, the researchers had access to rather rich data on their purchasing habits, which they were able to break down by race and job category. For the study, they analyzed purchases from December 2009 through August 2010. (According to Levy, the research team got permission from an ethics board to run the experiment without subjects’ consent, as long as their data was anonymized.)

According to the study, the labeling intervention led to an 11.2 percent overall decrease in the purchase of “red” foods and drinks, and a 6.6 percent increase in the purchase of “green” food and beverages. The one exception was Asians, whose results were ambiguous. The effects of the choice architecture intervention weren’t as clear—in part because the study could not separate the “convenience” variable out from the effects of the color coding.

The next step, Levy said, is a longer-term study that examines the next 18 months worth of data. Assuming the results hold up, what would explain why simple color coding does a better job of steering people in healthful directions than, say, explicit calorie counts?

In part, Levy said, it’s that many people just aren’t very good at math. “One of the reasons why we’re interested in doing it this way is that the data out there on numeracy and literacy shows that people, even with high literacy and numeracy, don’t necessarily understand nutritional labeling particularly well,” he said. “And certainly folks with lower numeracy and literacy would have more difficulty putting calorie numbers into context.”

That theory is supported by research into decision making, according to Julie Downs, an associate research professor at Carnegie Mellon who studies how and why people make decisions. “In order to use calorie information,” Downs said, “you really have to do math, and relatively complicated math.” For instance, a consumer might have to calculate calories multiple times a day, adding large numbers, subtracting calorie amounts based on exercise, and the like. In other words, it’s not as simple as it seems. “The prospect of using numbers is really asking for some pretty high cognitive engagement at every meal,” Downs said.

Colored labels, on the other hand, allow consumers to make quick, noncognitively-intensive choices. “It reduces the burden on the consumer hugely,” she said.

“The prospect of using numbers is really asking for some pretty high cognitive engagement at every meal.”

Richard Thaler, a University of Chicago Booth School of Business professor who co-wrote a book on how to nudge people toward more beneficial prudent eating decisions, said that even though calorie counts don’t appear to be effective, detailed nutritional information shouldn’t be neglected alltogether.

“You want to be moving in two directions at the same time,” Thaler said—providing the tools required for both quick, easy, on-the-fly decision making and more thoughtful, in-depth planning. What it comes down to, as he has argued both in his book and other writings, is three words: “make it easy.”

“There’s no hard theory that’s going to tell us what the best way to do this is,” he said. “A lot of this is common sense.”